Obesity is the number one health concern for pediatricians today. Almost 20% of children in the United Sates have a body mass index (BMI) = 95th percentile standard. The prevalence of obesity in New York City is particularly high and reached 31% in Hispanic and 23% in African American children in 2002-2003. One of the most important obesity-associated risks for children is obstructive sleep apnea syndrome (OSAS), with a reported prevalence rate between 46-59% compared with 2% in the general pediatric population. OSAS in turn, contributes to significant cardiovascular and cognitive morbidities in children. However, the pathophysiology of OSAS in obese children and why some obese children have OSAS while others do not is still unknown. Accelerated somatic growth may compromise airway size as well as airway collapsibility. Our team of pediatric researchers with expertise in sleep, pulmonology, public health, nutrition, and adolescent medicine, coupled with experts in the field of epidemiology and biostatistics, MRI, and biomechanics will study the anatomical, functional, and mechanical mechanisms leading to OSAS in inner city obese children 8-17 years of age using novel non-invasive methodologies. Our main focus will be to determine the anatomic and functional risk factors relating obesity to OSAS that have predictive value for distinguishing between obese children who will or will not have or develop OSAS. Further, we will determine how adenotonsillectomy and weight changes (both weight loss and weight gain) modify the above proposed mechanisms leading to OSAS in this group of children. Project Narrative: Obesity is the number one health concern for pediatricians today. One of the most important associated risks for obese children is obstructive sleep apnea syndrome (OSAS). This study will determine the anatomic and functional risk factors related to obesity and OSAS in inner city children 8-17 years of age using physiological studies coupled with novel imaging and computerized methodology.